Episode 14: The Science Of Sexual Development | Huberman Lab

Key Takeaways

  • A hormone has to be able to bind the receptor and take action on target cells to be effective
  • Testosterone and estrogen can travel into cells and interact with the DNA of cells to control gene expression
  • Primary sexual characteristics show up at birth (external genitalia) while secondary sexual characteristics take place during puberty (deepening of the voice, hair growth, etc.)
  • Masculinization of the brain in males and females is accomplished by estrogen via aromatase which converts testosterone to estrogen
  • Estrogen sets up masculine circuitry in the brain, testosterone controls the display of behaviors
  • In utero exposure to androgens may have an impact on mate selection and sexual orientation later in life
  • Pre-conception and in utero exposure to certain substances can impact the sexual characteristics of the fetus
  • The average density and volume of human sperm has decreased significantly in the U.S. and Europe

Introduction

Dr. Andrew Huberman, Ph.D. is a Professor of Neurobiology and Ophthalmology at Stanford University School of Medicine. His lab focuses on neural regeneration, neuroplasticity, and brain states such as stress, focus, fear, and optimal performance.

In this episode of Huberman Lab, Dr. Huberman discusses how hormones such as testosterone and estrogen and their derivatives impact development and maturation, lifestyle factors shown to significantly impact hormone pathways, the importance of estrogen for brain development, and how hormone exposure in the womb shapes our appearance.

Host: Andrew Huberman (@hubermanlab)

Hormone Overview And Development Of Fetus

  • Definition of hormone: released in one area of the body (usually from a gland) that travel and have effects on that gland and other tissues in the body
  • Hormones have direct effects on the brain, body, and spinal cord
  • Androgen: category of hormones, including testosterone
  • Chromosomal sex: in general – the XY chromosome is male and XX chromosome is female
  • Y chromosome has genes that suppress female reproductive organs, promote the formation of testes, inhibit müllerian ducts
  • The placenta itself is an endocrine organ
  • Gonadal sex: in general – if gonads are testes then the fetus is male; if gonads are ovaries then the fetus is female
  • Steroid sex: effect of steroid hormones (i.e., testosterone and estrogen) on traits such as the shape of the baby, human, genitalia, jaw

What Hormones Do

  • The hormone has to be able to bind the receptor and take action on target cells to be effective
  • Hormones have two categories of effects: fast and slow in terms of the effect on genes
  • Fast-acting hormones: cortisol, adrenaline
  • Slow-acting hormones: testosterone, estrogen – can signal and attach to a cell to induce quick effects but generally have long-term effects
  • Testosterone and estrogen can travel into cells and interact with the DNA of cells to control gene expression
  • Effects of hormones are seen in primary sexual characteristics (the ones you’re born with) and secondary sexual characteristics (show up in puberty)

Primary Sexual Characteristics In Males

  • Primary sexual characteristics show up at birth – external genitalia which defines sex
  • Enzyme dihydrotestosterone is actually what’s responsible for the development of the penis in baby’s that have an X and Y chromosome – not testosterone
  • Dihydrotestosterone masculinizes primary sex characteristics  
  • The brain has receptors for testosterone and estrogen
  • Masculinization of the brain is not accomplished by testosterone
  • Masculinization of the brain is accomplished by estrogen, not testosterone – testosterone is converted to estrogen by an enzyme called aromatase (made by body fat and neurons in the brain)
  • Estrogen sets up masculine circuitry in the brain, testosterone controls the display of behaviors later in life

Secondary Sexual Characteristics In Males

  • Testosterone is involved in the development of secondary sexual characteristics – deepening of the voice, growth of pubic hair
  • Dihydrotestosterone is responsible for facial hair but also lack of hair on the head
  • Speed of entry and exit from puberty might be worthwhile to study correlation to aging and longevity arc

In-Utero Effects Of Hormones On Sexual Preference

  • Study: young males (versus young females) have more auto-acoustic emissions as picked up by the device
    • Females who identify as lesbians had comparable auto-acoustic emission to males
  • In utero exposure to androgens may have an impact on sexual preference
  • This type of study has been replicated approximately six times and has shown interesting correlations
  • It’s possible the brain organizes early and impacts same- or the opposite- sex choices later in life

Environmental Factors In Sexual Characteristics

  • Maternal use of evening primrose oil and skin contact with infant or young males accelerated breast bud development
  • Primrose oil promoted estrogenic activity in the body
  • Atrazine exposure in water causes severe testicular malformation in the organ
  • Herbicides have negative effects by impacting the ratio of hormones in the mother or testes or father – and – direct effects altering fetus
  • The average density and volume of human sperm has decreased significantly in the U.S. and Europe

Lifestyle Factors In Sexual Characteristics & Child Development

  • THC and other things in cannabis promote significant activity in aromatase (which converts testosterone to estrogen)
  • Pot smokers have a higher rate of development of gynecomastia (male development of breasts)
  • Smoking marijuana during pregnancy can promote more circulating estrogen in the body of developing fetus
  • No peer-reviewed, quality studies that cell phones are bad for the brain – but – there is evidence of defects in ovarian and testicular development
  • Cell phone storage in males: chronic exposure to cell phone emitted waves on gonads could impact swimming speed and density, and testosterone levels
  • Cell phone storage in females: chronic exposure to cell phone emitted waves can impact estrogenic levels and regularity of cycle, and prolactin levels
  • Creatine promotes balding in some males because of its effects on dihydrotestosterone
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Notes By Maryann

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